It sounds like Titan Quest is just a horribly programmed game. Firstly, the 1950 Pro AGP is known to get good FPS with high settings on Oblivion @ 1024 x 768.
It's not really an argument or debate. Oblivion is just the #1 most taxing game on the market, and a 1950Pro for $200 can play it with high settings. (Not MAX, but high as in everything maxed but the texture distance, which seems to be the most taxing feature)
It's either you haven't optimized your programs for dual core (most need specific application patches, like games for example), your drivers or some kind of resource hog is running in your background or you're not telling us everything.
A 1950Pro shouldn't have a problem running any game that's out RIGHT NOW at high visual settings @ 1024 x 768, even WITH 4x AA enabled.
Aside from you obviously needing a new monitor. (I recommend either the Viewsonic 19" widescreen with 5 ms or the Hanns G 19" widescreen 5 ms, both at Newegg for about $185-190) You also need to clean out your system. Delete any resource taxing programs, maybe even back up and reformat, reinstall your games, and make sure this time you patch all your games to make sure they support dual core.
Buying a $300+ video-card and a new motherboard and still using a crappy 15" LCD is a horrible MasterCard commercial if you ask me, and to add to that, upgrading all those parts just because TitanQuest doesn't run well is a dumb idea too. Find out why it's not running right, because it's obviously not your video-card's fault.